The structure of the 5'-terminus of heterogeneous nuclear RNA and cytoplasmic mRNA will be determined in Novikoff hepatoma cells as a function of time after labeling with H3-methyl methionine. The relative distribution of structures with one and two 2'-O-methylnucleosides and other characteristics of 5'-terminal cap structures will be determined. Feline leukemia virus RNA will be studied to determine the presence or absence of methylation in internal positions as well as in 5'-terminal cap structures. BIBLIOGRAPHIC REFERENCES: Stuart, S.E., F. Rottman, and R.J. Patterson. Nuclear Restriction of Nucleic Acids in the Presence of ATP. Biochem. Biophys. Res. Comm. 62, 439 (1975). Gerard, G.F., P.M. Loewenstein, M. Green, and F. Rottman. Poly 2'-O-Methylcytidylic acid: A Specific Template for Detecting Reverse Transcriptase in Human Breast Tumors. Nature 256, 150 (1975).